Preparation of liquid alkylated pentaborane-9



nited States tet 3,114,774 Patented Dec. 17, 1063 [ice 3,114,774PREPARATION F HQUEE) ALKYLATED PENTABGRANE-Sl George E. Ryschhewitsch,Columbus, Ohio, assignnr, by

mesne assignments, to Olin Mathieson Chemical Corporation, a corporationof Virginia No Drawing. Filed Dec. 1, 1955, Ser- No. 550,461 10 Claims.(Cl. 260-6065) My invention relates to the manufacture of alkylatedpentaboranes and, in particular, to the alkylation of pentaborane-9 withmonoolefin hydrocarbons while the reactants are in admixture with analkane or mixture of alkanes. The products produced in accordance withthe method of my invention can be used as fuels when burned with air, asdescribed in the application of Chiras and Mezey, Serial No. 501,742,filed April 15, 1955.

It is known in the art to prepare pentaborane, which is a relativelystable, colorless liquid melting at 46.8 C. Pentaborane is a boronhydride or borane, and the art is aware that the burning of a boranewith oxygen liberates considerably more energy than the oxidation of acorresponding amount of hydrocarbon, producing very high flametemperatures. This suggests the use of pentaborane as a fuel of veryhigh energy content. Pentaborane sufiers from the disadvantage, amongother things, however, that it has a relatively high vapor pressure, itsvapor pressure being 66 mm. of mercury at 0 C. and its boiling point atatmospheric pressure being 58 C.

One of the objects of my invention is to provide a method for producingliquid alkylated pentaboranes which are less volatile and less toxicthan pentaborane-9 but at the same time approaching pentaborane-9insofar as heat of combustion is concerned. Thus, in accordance with myinvention, I have discovered that pentaborane-9 can be reacted withmonoolefin hydrocarbons containing from 2 to 5 carbon atoms while inadmixture with certain alkanes or mixtures thereof to provide alkylatedpentaboranes which are stable, relatively non-volatile liquids withconvenient handling characteristics. By this process, monoolefinhydrocarbons which are available at rather low cost and large tonnagescan be reacted with pentaborane-9 to form valuable alkylatedpentaboranes in yields which are substantially greater than those whichare obtained when the olefins and pentaborane are reacted not inadmixture with the alkanes.

The exact manner of the action of the alkanes in increasing the yield ofthe alkylation reaction is not known to me. Thus, the alkane may beacting as a solvent or as a solvent and catalyst. It has been shown,however, that substantial increases in the yield of alkylated productscan be obtained when pentaborane-9 is alkylated with the olefin in thepresence of the alkane, in comparison with the yield obtained when thepentaborane-9 is alkylated with the olefin but with the alkane absent.

The following example illustrates an embodiment falling within the scopeof my invention and is to be considered not limitative. In the example,the term millimoles signifies milligram moles.

EXAMPLE In this experiment 10.0 millimoles of pentaborane-9 wascondensed into a 60 ml. glass bulb which was immersed in a Dewar flaskfilled with liquid nitrogen (temperature 196 G). Then, 9.92 millimolesof isobutylene, followed by 12.1 millimoles of n-heptane, were condensedinto the bulb at the same temperature. At this temperature the reactantswere solids. The bulb was sealed, removed from the cooling flask,allowed to Warm to room temperature and then heated for 7 /2 hours at150 C. in a Fisher Isotemp oven. After being removed from the oven thebulb was allowed to cool to room temperature and then attached to avacuum line. In the next step it was cooled with liquid nitrogen andopened to the vacuum line.

A part of the crude product in the bulb was allowed to warm up and wasfractionated through a series of cold traps. In the first instance thematerial was allowed to pass through three traps, the first being heldat 63 C., the second at 78 C., and the third at -196 C. Through a seriesof additional fractionation operations carried out with cold traps,unreacted pentaborane-9 was finally isolated in the 78 C. trap and wasidentified by its vapor pressure which is 131 mm. of Hg at 15 .l C. Then-heptane fraction was finally separated in the 63 C. trap and wasidentified by its vapor pressure of 35.2 mm. of Hg at 20 C. The fractioncontaining the unreacted isobutene, as well as isobutane resulting fromthe reaction, was collected in the 196 C. trap. Analysis of thisfraction in standard gas analysis equipment showed that this fractioncontained 0.07 millimole of isobutane and 5.00 millimoles of isobutene.The quantity of unreacted pentaborane-9 caught in the 78 C. trap was8.54 millimoles.

The remaining material in the bulb was fractionated through a series offour cold traps held at 20 C., 52 C., 78 C. and 196 C., respectively.The fraction obtained in the 52 C. trap was refractionated through threetraps held at 63 C., 78 C. and -196 C., respectively. After a series ofrefractionation operations a fraction was obtained in a 52 C. trap whichexhibited a vapor pressure of 5 mm. of Hg at 25 C. which is identical tothe vapor pressure of pure iso-butylpentaborane. The weight ofiso-butylpentaborane collected in the 52 C. trap was 1.19 millimoleswhich corresponds to a yield of 78.3 percent based on the pentaborane-9used in the reaction. The remainder of the pentaborane-9 consumed wastransformed into tri-isobutylborane and other viscous liquids containingcarbon which are not volatile at room temperature. The amount oftri-iso-butylborane formed as recovered in the 20 C. trap was 0.61millimole.

A control run in which n-heptane was not present was also carried outand a comparison of the results obtained in Example I and the controlrun is given in Table I below.

Various modifications can be made in the procedures of the specificexample to provide other embodiments which fall within the scope of myinvention. Thus, in place of the isobutylene utilized, there can besubstituted other monoolefin hydrocarbons having from 2 to 5 carbonatoms, for example, ethylene, propylene, l-butene, 2- butene and thelike, as well as mixtures thereof. Also, in place of the n-heptane,there can be substituted other saturated aliphatic hydrocarbonscontaining from 6 to 10 carbon atoms, for example, n-hexane, noctane,2,2,3-

trimethylpentane, 2,2,4-trimethylpentane, n-decane and the like, as wellas mixtures thereof.

In general, the reaction temperature employed will be within the rangefrom about 130 C. to about 190 C., although somewhat higher as Well assomewhat lower reaction temperatures can be used. In like manner, thereaction time can be varied widely, generally being within the rangefrom about 1 to about 24 hours and preferably within the range fromabout 4 to about 8 hours. The ratio of olefin to pentaborane-9 utilizedin carrying out my process can be varied widely, generally being withinthe range from 0.1 .to 10 moles of olefin per mole of pentaborane-S. Thepreferred range of olefin to pentaborane-9 employed is from 0.5 to 2.0moles of olefin to 1 mole of pentaborane-9, depending upon the degree ofalkylation desired. The quantity of saturated aliphatic hydrocarbon,such as n-heptane, used will generally vary from about 1 to moles ofsuch hydrocarbon to 1 mole of pentaborane-9.

I claim:

1. A method for the preparation of a liquid reaction product ofpentaborane-9 and a monoolefin hydrocarbon having from 2 to 5 carbonatoms which comprises reacting from 0.1 to moles of the monoolefinhydrocarbon per mole of the pentaborane-9 at a temperature Within therange from 130 to 190 C. While the reactants are in admixture with from1 to 5 moles, per mole of pentaborane-9, of at least one saturatedaliphatic hydrocarbon containing from 6 to 10 carbon atoms.

2. The method of claim 1 wherein said monoolefin hydrocarbon isethylene.

3. The method of claim 1 wherein said monoolefin hydrocarbon isisobutylene.

4. The method of claim 1 wherein said monoolefin hydrocarbon ispropylene.

5. The method of claim 1 wherein said saturated aliphatic hydrocarbon isn-heptane.

6. A method for the preparation of a liquid reaction product ofpentaborane-9 and a monoolefin hydrocarbon having from 2 to 5 carbonatoms which comprises reacting from 0.5 to 2 moles of said monoolefinhydrocarbon per one mole of pentaborane-9 at a temperature within therange from to C. while the reactants are in admixture with from 1 to 5moles, per mole of pentaborane-9, of at least one saturated aliphatichydrocarbon containing from 6 to 10 carbon atoms.

7. The method of claim 6 wherein said monoolefin hydrocarbon isethylene.

8. The method of claim 6 wherein said monoolefin hydrocarbon isisobutylene.

9. The method of claim 6 wherein said monoolefin hydrocarbon ispropylene.

10. The method of claim 6 wherein said saturated aliphatic hydrocarbonis n-heptane.

References Cited in the file of this patent Hurd: J. Amer. Chem. Soc.70, pages 2053-2055.

1. A METHOD FOR THE PREPARATION OF A LIQUID REACTION PRODUCT OFPENTABORANE-9 AND A MONOOLEFIN HYDROCARBON HAVING FROM 2 TO 5 CARBONATOMS WHICH COMPRISES REACTING FROM 0.1 TO 10 MOLES OF THE MONOOLEFINHYDROCARBON PER MOLE OF THE PENTABORANE-9 AT A TEMPERATURE WITHIN THERANGE FROM 130* TO 190* C. WHILE THE REACTANTS ARE IN ADMIXTURE WITHFROM 1 TO 5 MOLES, PER MOLE OF PENTABORANE-9, OF AT LEAST ONE SATURATEDALIPHATIC HYDROCARBON CONTAINING FROM 6 TO 10 CARBON ATOMS.